(You can get the loyalty symbols by enclosing them in square brackets: so [+1] rather than +1.)

I'm finally happy with him. I feel that I have the most trouble designing Planeswalkers out of all card types.

Planeswalkers are extremely difficult to design, certainly. But this looks like a reasonable design. Perhaps a little unexciting due to being so focused, but Nissa Revane and Tezzeret, Agent of Bolas say it's okay to have focused planeswalkers occasionally.

I'm not too keen on the ultimate, because it's a bit like saying "Target player concedes." But I admit, it's not a game winner in multi-player, and the game might still be alive after that. It certainly feels like an ultimate, which is good. Too many people design Planeswalkers that are difficult to go ultimate, then for a final ability, they toss out a 4 casting cost ability. Wrath of God may be a good spell, but it's just a punch in the gut. Ultimates need to be a flying punch in the gut, stay levitating with your fist in the opponent's gut, then slowly rotate.

@jmg: One point in favour of the ultimate is that it's an ability that's been seen on a printed card: Gilt-Leaf Archdruid.

It's a very green ultimate though. But the target land destruction bit is very red, so I forgive it.

An "I win" ultimate at rr2 +5 turns even if interrupted? yeah, that's probably allowed.

I'm not sure it is that green. "Gain control of" is vanishingly rare in green - the Archdruid is virtually the only example. Red and blue have both done gaining control of lands: Conquer, Annex - so I think this is fine.